x86/efi: Only map RAM into EFI page tables if in mixed-mode

x86/efi: Only map RAM into EFI page tables if in mixed-mode

Waiman reported that booting with CONFIG_EFI_MIXED enabled on his
multi-terabyte HP machine results in boot crashes, because the EFI
region mapping functions loop forever while trying to map those
regions describing RAM.

While this patch doesn't fix the underlying hang, there's really no
reason to map EFI_CONVENTIONAL_MEMORY regions into the EFI page tables
when mixed-mode is not in use at runtime.

Reported-by: Waiman Long <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Linus Torvalds <[email protected]>
CC: Theodore Ts'o <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Scott J Norton <[email protected]>
Cc: Douglas Hatch <[email protected]>
Cc: <[email protected]> # v4.6+
Signed-off-by: Matt Fleming <[email protected]>